A reaction at 1 bar is non–spontaneous at low temperature but becomes...
Explanation:
The spontaneity of a reaction is determined by the change in Gibbs free energy (ΔG) which is given by the equation:
ΔG = ΔH - TΔS
Where:
ΔG = Gibbs free energy change
ΔH = Enthalpy change
T = Temperature in Kelvin
ΔS = Entropy change
If ΔG is negative, the reaction is spontaneous. If ΔG is positive, the reaction is non-spontaneous.
In this case, the statement says that the reaction is non-spontaneous at low temperature but becomes spontaneous at high temperature. This means that at low temperature, ΔG is positive but at high temperature, ΔG becomes negative.
To determine the sign of ΔG, we need to consider the signs of ΔH and ΔS.
ΔH and ΔS:
- ΔH represents the change in enthalpy, which is the heat energy absorbed or released during a reaction. If ΔH is negative, it means that the reaction releases heat and is exothermic. If ΔH is positive, it means that the reaction absorbs heat and is endothermic.
- ΔS represents the change in entropy, which is a measure of the randomness or disorder of a system. If ΔS is positive, it means that the reaction increases the randomness of the system. If ΔS is negative, it means that the reaction decreases the randomness of the system.
Analysis:
- At low temperature, the reaction is non-spontaneous, which means that ΔG is positive. To make ΔG positive, either ΔH must be positive or TΔS must be negative.
- At high temperature, the reaction becomes spontaneous, which means that ΔG is negative. To make ΔG negative, either ΔH must be negative or TΔS must be positive.
Conclusion:
Since the reaction becomes spontaneous at high temperature, it means that TΔS is positive. Therefore, the correct statement is that both ΔH and ΔS are positive (option D). This means that the reaction is endothermic (ΔH > 0) and increases the randomness of the system (ΔS > 0) at high temperature.
A reaction at 1 bar is non–spontaneous at low temperature but becomes...
∆G = ∆H-T∆S
For a spontaneous reaction ∆G = -ve
which is possible when both ∆H and ∆S are positive at high temperature and hence the reaction becomes spontaneous.
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